1. Field of the Invention
The present invention relates to an improved heat exchanger finned tube and method and apparatus for producing said finned tube and more particularly, but not by way of limitation, to a finned tube which comprises spirally wrapped fin stock material around tubing stock with a double knurling operation to provide intimate contact of the fin stock with the tubing material to insure maximum durability and conductivity.
2. History of the Prior Art
There has been considerable effort expended to produce heat exchanger finned tube material for use with various forms of heat exchangers, radiators and the like. The major portion of finned tube material comprises thin metal strips of stock or plate material attached to the outer surface of a tube or pipe in order to effectively increase the surface area of the tube for either expelling heat from or conducting heat to a fluid carried within the tube or pipe.
Fin stock has been attached to the fluid carrying tube by various techniques, including welding, brazing, soldering, gluing and even tightly wrapping the fin stock about the outer surface of the tube.
Three different basic configurations have been utilized in producing fin stock material, one being to weld longitudinal strips of fin stock material about the outer surface of the tube; the second being to place a plurality of washer-like discs of fin material about the tube and welding them in a spaced relation along the tube; and the third being to spirally wrap the fin stock material about the outer surface of the tube.
A considerable portion of the finned tube produced comprises aluminum fin stock which is attachable to various types of central tubes. Aluminum is a widely used fin stock material and has the characteristics of being somewhat malleable and yet heat conductive.
As stated, in some applications the fin stock material is spirally wound tightly about the central tube. However, when such material fails due to thermal shock conditions or other causes of failure, often a significant portion of the fin becomes unwound and cannot be repaired on the site. Another problem associated with presently produced finned tube is that there are often gaps or separation points between the fin stock and the tube thereby interrupting heat conductivity and reducing the effectiveness of the finned tube.
The use of welding techniques to secure the fin stock to the tube helps prevent failure due to separation of the fin stock from the tube but is extremely expensive and, in the use of aluminum fin stock, welding techniques require sensitive MIG or TIG welding equipment.
The use of adhesive to secure the fin stock to the tube serves to more firmly attach the fin stock but often has an insulative effect between the fin stock and the tube, again, reducing the effectiveness of the finned tube as a heat conductor.
Presently used apparatuses for producing spirally wound finned tubing material typically require two or more operators per finning machine in order to handle the finned tube that is produced on the machine. Typically, at least one operator is required to devote his full attention to the finning head area of the machine while another operator must be involved in the handling of the completed finned tubes and sawing the tubes to length. Further, if the central tubing used to form the fin stock is to be cut during the middle of an operation, the entire finning operation must be stopped while the material is cut to the desired length. Therefore, the use of multiple operators for producing fin stock material causes the end product to be expensive, a large portion of which is due to labor costs.